1. Field of the Invention
The present invention relates to an image forming system such as a recording apparatus, copying machine, or the like. In particular, it relates to an image forming system wherein cassettes having different sizes can be replaceable.
2. Related Background Art
In order to increase a recording sheet containing amount in conventional recording apparatuses, as shown in FIG. 21, an additional sheet supply means c is provided at a bottom of a body frame a of a recording system, and an additional sheet supply cassette b is mounted within the recording system below the additional sheet supply means. Alternatively, as shown in FIG. 22, an additional sheet supply unit f having a sheet supply means (not shown) and to which a sheet supply cassette e is attached, can be mounted on a front side of a body frame d of a recording system.
In FIGS. 21 and 22, the letters g, h denote image forming cartridges; and i, j denote optical systems for scanning laser beams emitted in response to external signals by respective polygonal mirrors and for illuminating respective photosensitive drums in the cartridges g, h with the scanned laser beams, respectively. Further, images formed on recording sheets supplied from the standing or permanent sheet supply cassettes and from the additional sheet supply cassettes b, e are fixed by fixing devices k, 1, respectively. The recording sheets to which the images were permanently fixed are ejected onto an upper ejection tray m (FIG. 21) and a rear ejection tray n, FIGS. 22 respectively.
However, in increasing the recording sheet containing amount in the above-mentioned conventional manners, in addition to the provisions of the additional sheet supply cassette b or e, it is necessary to further provide a separating and supplying means for separating and supplying the recording sheets in the additional cassette. Additionally, a motor for driving such separating and supplying means, and a clutch means for connecting/disconnecting the output of the motor are required, and electric control parts and wirings for such motor and clutch are also required. Therefore, conventionally, the user had the great expense for increasing the recording sheet containing amount, in addition to the expense for preparing accessories for the recording apparatus.
To avoid this, a recording apparatus wherein a sheet supply cassette can be attached to legs of a body frame of the apparatus and the sheet supply cassette can be replaced by another sheet supply cassette having different sheet containing ability by changing the legs has been proposed, as disclosed in the Japanese Utility Model Laid-Open No. 60-8954. More particularly, in this recording apparatus, as shown in FIGS. 23A and 23B, a plurality of kinds of leg members, T.sub.1, T.sub.2 are prepared for support legs of a body frame a of the apparatus, and the leg members T.sub.1, T.sub.2 have guides for mounting sheet supply cassettes b.sub.1, b.sub.2 corresponding to the heights of the leg members T.sub.1, T.sub.2, respectively. When the normal sheet supply cassette b.sub.1 is used, the leg members T.sub.1 are coupled to the body frame a (as shown in FIG. 23A), and when the larger sheet capacitive cassette b.sub.2 is used, the leg members T.sub.2 are coupled to the body frame a (as shown in FIG. 23B). In this way, the sheet s cassettes having different sheet containing abilities can be mounted on the recording apparatus.
Further, a recording apparatus wherein the heights of leg members for supporting a body frame of the apparatus are adjustable so that sheet supply cassettes having different sheet containing abilities can be mounted on the bottom of the apparatus has also been proposed, as disclosed in the Japanese Utility Model Laid-Open No. 60-59264.
However, with these arrangements, it was feared that the leg members were distorted or bent at the coupling point to the body frame by the weight of the cassette. If the leg members are distorted or bent, the contacting pressure (sheet supplying pressure) between the sheet supply means and the sheets in the cassette will be changed, thus causing the poor sheet to feed easily. To avoid this, the coupling strength between the leg members and the body frame must be increased and the rigidity of the leg member itself must be increased, which results in the increase in the weight and cost of the apparatus and/or makes the apparatus complicated.